The invention generally relates to the preservation of a predetermined dose of liquid-based substance, in particular pure or diluted animal semen; and more particularly to the straws for performing such preservation.
It is known that such a straw comprises a tube and a stopper disposed in the tube. The stopper is usually of the three-part type originally described in French patent 995.878, corresponding to British patent 669,265, i.e. formed by two plugs made from a fibrous substance enclosing a powder which, on contact with a liquid, transforms into an impermeable paste or gel adhering to the wall of the tube so that the stopper is liquid-tight.
Similar but improved stoppers are described by the French patent applications 2 824 255 and 2 824 256.
Stoppers of another type are also known, for example a stopper made from a single-piece cylinder of hydrophobic microporous material described by European patent application 0 873 726 or a stopper made from a single-piece cylinder of sintered self-sealing microporous material as described by PCT application WO 2010/070533.
In the initial state, the stopper is disposed in the neighborhood of one of the ends of the tube and it is provided that in the filled state, the dose of liquid substance which must be preserved in the straw is disposed between the stopper and the other end of the tube (the end furthest from the stopper).
To fill the straw, the end closest to the stopper is placed in communication with a vacuum source while the furthest end of the tube is placed in communication with a vessel containing the substance to be introduced into the straw.
The air initially contained between the stopper and the furthest end of the tube is sucked through the stopper while the substance moves forward into the tube until it meets the stopper.
If necessary, after filling, the straw is welded close to one or both of its ends and is stored cold.
In order to empty the straw, if necessary after cutting the welded end portions and thawing, a rod is inserted into the tube via the end closest to the stopper, until it bears against the stopper. Using this rod, the plug is made to slide in the manner of a piston towards the end furthest from the stopper, which causes the expulsion of the dose of substance which had been introduced into the straw.
When the straw is used to preserve diluted animal semen, in particular bovine semen, emptying of the straw is carried out to perform an artificial insemination.